1. Water leakage in underground engineering can cause the loss of calcium hydroxide within the reinforced concrete, leading to a decrease in pH levels. This makes the steel bars within the concrete structures prone to corrosion and accelerates the alkali-aggregate reaction in the concrete, thereby affecting structural safety and shortening the lifespan of the project.
2. Water leakage in underground engineering can lead to the loss of its usability. Prolonged work or living in a damp environment can easily result in radon contamination, affecting health and potentially leading to loss of work capacity; for storage purposes, it can cause goods to become damp, rot, deteriorate, or become ineffective.
3. Leaks in underground engineering require year-round mechanical drainage and the use of dehumidifiers or desiccants to control moisture, both of which lead to energy loss and skyrocketing costs.
4. A leakage in the water conveyance tunnel not only results in a loss of water volume and an increase in conveyance costs, but also causes soil around the tunnel to collapse, forming voids, which endangers the structural safety of the water conveyance tunnel.
Therefore, conducting research, analysis, and studies on the treatment technology for leakage and seepage in special underground engineering, proposing feasible implementation plans, and applying these to engineering projects holds significant practical importance. During the construction using the shield method, tunnels assembled from reinforced concrete segments (lining) may experience leakage and seepage due to various reasons. To ensure the quality of the tunnel engineering, it is essential to carry out waterproofing and leakage prevention treatments. The tunnel waterproofing and leakage prevention technique has summarized nearly 30 years of experience in tunnel leakage prevention from both theoretical and practical perspectives. This technique has been applied in major projects such as the Shanghai Metro Line 1 inter-tunnel, Yan'an East Road River Crossing Tunnel, Dapu Road River Crossing Tunnel, and Jinshan Petrochemical Plant's inlet and outlet tunnel, achieving the goals of stopping water and preventing leakage, and yielding good social and economic benefits. The water-soluble polyurethane grouting material used in this technique received the Third Prize for Science and Technology Progress from the Ministry of Construction.
Feature
1.1 The waterproofing and leakage prevention techniques effectively address issues such as leakage, stopping water, and waterproofing in underground engineering, including joints, construction joints, deformation joints, honeycomb surfaces, and shrinkage cracks in concrete structures. The results are notably effective in preventing water seepage.
The 1.2 waterproofing and leak-proofing construction method is simple and effective, with compact equipment that is not restricted by the size of the construction site.
The grouting materials and sealant materials currently used in the 1.3 waterproofing and leakage prevention techniques, such as oil-soluble and water-soluble polyurethane grouting materials, 821BF water-expanding rubber, 888 bentonite sealant, etc., have all reached the advanced level domestically, with some having reached international standards.
In the 1.4 waterproofing and leakage prevention technique, special processes and materials can reinforce concrete cracks, particularly addressing the fine cracks resulting from the shrinkage of large-scale poured concrete.
Scope of Application
Waterproofing and leakage prevention construction for various underground projects, including civil air defense basements, underground tunnels, and underground parking garages.
The basic principle of the waterproofing and leak-sealing technique used is chemical grouting. Chemical grouting involves injecting specially formulated grout materials into the structural cracks of buildings using manual or mechanical methods under pressure. This causes the grout to solidify within the cracks, achieving the purpose of filling the cracks and stopping leaks. For through cracks, methods such as sealing the crack, burying pipes, and chemical grouting can be adopted. For non-through cracks, due to the airtightness, it is difficult to inject the grout into the apex area of the crack, thus unable to eliminate the stress concentration area formed there. Therefore, various factors should be carefully considered during the treatment to improve the filling rate of the grout. For temperature cracks, considering the "lag effect" of concrete structures on temperature, it is generally recommended to perform grouting treatment at the low point of the concrete body temperature for better results.
4 Waterproof Construction Techniques
4.1 Flexible Waterproofing and Leak Sealing Construction Technique: Waterproofing construction involves several steps including cutting joints, removing slots, sanding, and applying coatings, as shown in Figure 1.
4.1.1 Cutting and Grooving: According to design specifications, first cut along the edges of the pipe sections using a cutting machine, then drill grooves with an impact drill, and finally, refine them manually to create a 5cm deep groove.
4.1.2 Surface Treatment: Surface treatment is conducted using two methods. For areas with obvious water leakage, drilling and grouting is employed to block water (using polyether grout or water-soluble polyurethane as the grouting material). For other leaky areas, rapid-hardening cement is used for sealing. The SH external agent for rapid-hardening cement is mixed with 425# ordinary portland cement in proportion, or double-rapid cement is used. Subsequently, the sealing process is carried out. The setting time of the cement is adjusted to approximately 2 minutes.
4.1.3 Sanding: Use a wet grinding machine to sand the area approximately 20cm wide on both sides of the segment joints. Remove irregularities, debris, and dust. Sanding reveals a fresh, smooth concrete base, laying the groundwork for the next step of applying waterproofing paint. 4.1.4 Sealing: Inject the mixed 851 tar polyurethane sealant or 888 bentonite sealant, or FUP polyurethane sealant series waterproofing materials into the repaired grooves until the surface of the pipe segments is level. After sealing, use a scraper to press and smooth the sealant to enhance the bond between the sealant and the concrete.
4.1.5 Application of Waterproof Coating Layer To protect the filling material and enhance the waterproofing capability of the pipe segment joints, apply 2 to 3 layers of flexible waterproof coating on both sides of the joints. The film thickness of the waterproof coating should be maintained at 2mm, and attention should be paid to forming an integral waterproof film during application; it can be evenly coated with a spatula or brush: or use chloroprene latex polymer mortar as the external waterproof layer. The filling and coating of the waterproofing layer should be carried out in a non-leaking, dry condition. 4.2 Combining Flexible and Rigid Waterproofing Sealing Technique The procedure for combining flexible and rigid waterproofing sealing technique is as follows: abrading, cutting, grooving; pulling tubes, filling joints, smoothing, and grouting. See Figure 2.
4.2.1 Deburring, Grooving, and Chiseling: Deburring involves manually using chisels to create grooves on both sides of the pipe joints, each 20cm wide, to expose the fresh concrete surface and make it rough. This enhances the adhesion between the rigid mortar and the concrete. Grooving and chiseling are performed using a diamond-tipped concrete saw with a cutting width of 4-5cm and a groove depth of 5-6cm. The grooves are then finished with an impact drill, using a shovel and manual finishing to create grooves 5-6cm deep. 4.2.2 Pipe Extraction: A φ14mm PVC hose is used as a mold. Double-quick cement or other rapid-setting cement is used to seal the joints and perform the pipe extraction. A lead water grouting pipe is left at the end.
4.2.3 Available Joint Sealing Materials: (1) Epoxy Coal Tar Paint (base amine and sealant) (2) 851 Coal Tar Polyurethane Paint (3) TPC Polyurethane Sealant Series Waterstop Materials; First, clean the grooves and sides of loose dust and soil with wire brushes and bristle brushes, then insert the joint sealing materials (during construction, follow various joint sealing procedures)
